1. Field of the Invention
The present invention relates to a stator for an alternator driven by an internal combustion engine, for example, and in particular, relates to a stator construction for an automotive alternator mounted to an automotive vehicle such as a passenger car or a truck.
2. Description of the Related Art
FIG. 20 is a cross section showing a conventional automotive alternator.
In FIG. 20, the automotive alternator includes: a case 3 composed of an aluminum front bracket 1 and an aluminum rear bracket 2; a shaft 6 rotatably mounted inside the case 3, a pulley 4 being fastened to a first end of the shaft 6; a Lundell-type rotor 7 fastened to the shaft 6; fans 5 fastened to first and second axial ends of the stator 78; a stator 8 fastened to an inner wall of the case 350 as to cover an outer circumferential side of the rotor 7; slip rings 9 fastened to a second end of the shaft 6 for supplying electric current to the rotor 7; a pair of brushes 10 which slide in contact with the slip rings 9; a brush holder 11 for holding the brushes 10; a rectifier 12 which is electrically connected to the stator 8 to convert alternating current generated in the stator 8 into direct current; a heat sink 17 fitted onto the brush holder 11; and a regulator 18 mounted on the heat sink 17 for adjusting the magnitude of an alternating voltage generated in the stator 8.
The rotor 7 is composed of a rotor coil 13 for generating magnetic flux on passage of electric current, and a pair of pole cores 20 and 21 disposed so as to cover the rotor coil 13, magnetic poles being formed in the pole cores 20 and 21 by magnetic flux generated in the rotor coil 13. The pair of pole cores 20 and 21 are made of iron, each has eight claw-shaped magnetic poles 22 and 23 disposed on an outer circumferential perimeter at even pitch in a circumferential direction so as to project axially, and the pole cores 20 and 21 are fastened to the shaft 6 facing each other such that the claw-shaped magnetic poles 22 and 23 intermesh.
The stator 8 is provided with a stator core 15, and a stator coil 16 which generates alternating current due to changes in magnetic flux produced by the rotor coil 13 accompanying the rotation of rotor 7 wound to the stator core 15.
In the automotive alternator constructed in this manner, electric current is supplied from a battery (not shown) through the brushes 10 and the slip rings 9 to the rotor coil 13, generating magnetic flux. The claw-shaped magnetic poles 22 of the first pole core 20 are magnetized with north-seeking (N) poles by this magnetic flux, and the claw-shaped magnetic poles 23 of the first pole core 21 are magnetized with south-seeking (S) poles.
At the same time, rotational torque from the engine is transmitted through the belt and the pulley 4 to the shaft 6, rotating the rotor 7. Thus, a rotating magnetic field is applied to the stator coil 16, generating electromotive force in the stator coil 16. This alternating electromotive force passes through the rectifier 12 and is converted into direct current, the output is adjusted by the regulator 18, and the battery is recharged.
When generating electricity, the rotor coil 13, the stator coil 16, the rectifier 12, and the regulator 18 continuously generate heat. In an alternator having a rated output current in the 100A class, these components generate 60W, 500W, 120W, and 6W of heat, respectively at rotational points at which the temperature is high.
In order to cool this heat produced due to the generation of electricity, air intake openings 1a and 2a are disposed in axial end surfaces of the front bracket 1 and the rear bracket 2, and air discharge openings 1b and 2b are disposed in two outer circumferential shoulder portions of the front bracket 1 and the rear bracket 2, opposite the radial outside of the front-end and rear-end coil end groups 16f and 16r of the stator coil 16.
At the rear end, external air is drawn in through the air intake openings 2a disposed opposite the heat sink of the rectifier 12 and the heat sink 17 of the regulator 18, respectively, by rotation of fans 5, flowing along the axis of the shaft 6, cooling the rectifier 12 and the regulator 18, and is then deflected centrifugally by the fans 5, cooling the rear-end coil end group 16r of the stator coil 16 before being expelled to the outside through the air discharge openings 2b. At the same time, at the front end, external air is drawn in axially through air intake openings 1a by rotation of the fans 5, and is then deflected centrifugally by the fans 5, cooling the front-end coil end group 16f of the stator winding 16 before being expelled to the outside through the air discharge openings 1b. 
Next, a method of winding the stator coil 16 will be explained with reference to FIG. 22. Moreover, for convenience, the method of winding a coil having one turn is shown in FIG. 22.
The stator coil 16 is constructed by connecting in series a number of coil segments 30 (strands of wire) composed of a copper material, for example, which are short electrical conductors having a flat cross section coated with insulation. Each coil segment 30 is formed into a general U shape composed of a pair of straight portions 30a connected by a V-shaped turn portion 30b. 
The coil segments 30 are inserted from the rear end two at a time into sets of slots 15a three slots apart. At that time, four straight portions 30a are housed in each of the slots 15a so as to line up in one row in a radial direction. The coil segments 30 on an inner circumferential side are each inserted into a first position from the inner circumferential side (hereinafter called xe2x80x9cthe first addressxe2x80x9d) of first slots 15a, and inserted into a second position from the inner circumferential side (hereinafter called xe2x80x9cthe second addressxe2x80x9d) of second slots 15a three slots away, and the coil segments 30 on an outer circumferential side are each inserted into a third position from the inner circumferential side (hereinafter called xe2x80x9cthe third addressxe2x80x9d) of the first slots 15a, and inserted into a fourth position from the inner circumferential side (hereinafter called xe2x80x9cthe fourth addressxe2x80x9d) of the second slots 15a three slots away. In other words, the coil segments 30 are housed within the sets of slots 15a three slots apart so as to form different layers.
Next, the free ends 30c of the coil segments 30 extending outwards at the front end are bent to open outwards (circumferentially outwards) so as to be at a constant angle relative to the direction of the grooves of the slots 15a, and in addition, the free ends 30c are each bent so as to extend in the same axial direction as the stator core 15. Then, with apex portions of the turn portions 30b of each of the coil segments 30 positioned so as to be at the same height, the free ends 30c of the coil segments 30 extending outwards at the front end from the first address within the slots 15a and the free ends 30c of the coil segments 30 extending outwards at the front end from the second address within the slots 15a three slots away are stacked radially and joined by welding. Thus, two inner circumferential coils are obtained by connecting in series a number of the coil segments 30 which are housed in a first slot group constituted by every third slot 15a. 
Similarly, the free ends 30c of the coil segments 30 extending outwards at the front end from the third address within the slots 15a and the free ends 30c of the coil segments 30 extending outwards at the front end from fourth address within the slots 15a three slots away are stacked radially and joined together by welding. Thus, two outer circumferential coils are obtained by connecting in series a number of the coil segments 30 which are housed in the first slot group constituted by every third slot 15a. 
These inner circumferential and outer circumferential coils are connected in series to form one coil phase portion having four turns.
A number of coil segments 30 housed in a second slot group constituted by the slots 15a offset by one slot from the slots 15a of the first slot group are similarly connected to form one coil phase portion having four turns. In addition, a number of coil segments 30 housed in a third slot group constituted by the slots 15a offset by one slot from the slots 15a of the second slot group are similarly connected to form one coil phase portion having four turns. These three coil phase portions are connected into an alternating-current connection to form the stator coil 16.
In this manner, the stator 8 is obtained by winding the stator coil 16 into the stator core 15 as shown in FIG. 21.
At the front end of the stator core 15, the insulation coating is stripped from the free ends 30c of the coil segments 30 in advance, as shown in FIGS. 23 and 24, and the free ends 30c of the coil segments 30 are stacked on top of one another radially then arc welded from above, aiming at a contact point A between pairs. Thus, pairs of the coil segments 30 are electrically connected through melted portions 31 on upper portions of the free ends 30c. Coil ends are formed by a connection pattern in which electrical conductors in different addresses in pairs of slots three slots apart are connected in series, the connection pattern being obtained by bending and welding together the free ends 30c of the coil segments 30 extending outwards from the pairs of slots three slots apart. These coil ends are arranged around the stator core 15 with a predetermined pitch in a circumferential direction to constitute a front-end coil end group 16f. Thus, cooling air deflected centrifugally by the fans 5 enters the front-end coil end group 16f through gaps between the coil ends and flows smoothly along the surfaces of the electrical conductors which form the coil ends, effectively cooling the front-end coil end group 16f. 
At the same time, at the rear end of the stator core 15, coil ends are formed by a connection pattern in which electrical conductors in different addresses in pairs of slots three slots apart are connected in series, the connection pattern being obtained by the turn portions 30b of the coil segments 30. These coil ends are arranged around the stator core 15 with a predetermined pitch in a circumferential direction to constitute a rear-end coil end group 16r. Thus, cooling air deflected centrifugally by the fans 5 enters the rear-end coil end group 16r through gaps between the coil ends and flows smoothly along the surfaces of the electrical conductors which form the coil ends, effectively cooling the rear-end coil end group 16r. 
Because automotive alternators equipped with stators 8 constructed in this manner are installed in engines with a high degree of vibration, the failures described below have occurred easily, leading to problems of reduced reliability and performance.
First, the insulation coating is stripped from the free ends 30c of the coil segments 30. Because the turn portions 30b of the coil segments 30 are formed by bending short segments of copper wire material coated with an insulation coating, bending stress is concentrated at the apex portions of the turn portions 30b, increasing the likelihood of damage to the insulation coating. Because the stator coil 16 has electrical potential during power generation and the coil end groups 16f and 16r are in close proximity to the brackets which are earthed, there is a risk that electrolytic corrosion will occur on exposed portions of the electrical conductors at the apex portions of the turn portions 30b and at the free ends 30c, leading to wire breakages due to vibration.
Furthermore, because the free ends 30c are joined together by arc welding, the melted portions 31 are formed so as to protrude. In other words, the melted portions 31 rise up from end surfaces of the free ends 30c and jut out horizontally. Thus, the spacing S2 between the joint portions of the free ends 30c becomes narrower and there is a risk of layer short-circuiting due to vibration. In addition, if layer short-circuiting occurs during power generation, stator current is disturbed, thereby also disturbing a magnetic flux wave form in an air gap between the stator 8 and the rotor 7 which is a factor causing magnetic attraction. Thus, magnetic attraction increases, giving rise to excessive electromagnetic noise.
Furthermore, the welded portions of the free ends 30c may be dislodged by vibration, or cracking may occur, increasing connection resistance, thereby making the temperature of the stator coil 16 excessively high.
In addition, because the front-end coil end group 16f is positioned on a side of the fans 5 where the cooling air is discharged, wind noise occurs due to unpleasant high-order interference noise arising between the shoulder portions of the claw-shaped magnetic poles 22 and 23 and the fans 5 due to the complexly-shaped melted portions 31.
The present invention aims to solve the above problems and an object of the present invention is to provide a stator for an alternator in which reliability and performance can be improved without reducing cooling of the coil end groups by eliminating exposure of the electrical conductors by applying an electrically-insulating resin portion to the apex portions of the coil ends.
In order to achieve the above object, according to one aspect of the present invention, there is provided a stator for an alternator, the stator including:
a cylindrical stator core formed with a number of slots extending axially at a predetermined pitch in a circumferential direction; and
a stator coil installed in the stator core,
the stator coil including a number of winding sub-portions,
each of the winding sub-portions being installed in the stator core by housing electrically-insulated strands of wire in slots a predetermined number of slots apart so as to form different layers relative to a slot depth direction and connecting the different layers in the slots the predetermined number of slots apart to each other in series outside the slots in a predetermined connection pattern to form coil ends,
the coil ends being aligned and mutually spaced circumferentially to constitute two coil end groups of the stator coil,
an electrically-insulating resin portion being formed by applying a resin so as to cover surfaces of apex portions of the coil ends constituting at least one of the two coil end groups while ensuring air passage spaces between circumferentially-adjacent coil ends.
The coil ends in each of the two coil end groups may be arranged circumferentially around the stator core so as to line up in two rows radially.
The apex portions of the coil ends may be arranged in a zigzag formation.
Spaces between the radially adjacent apex portions of the coil ends of the stator core may be filled by the electrically-insulating resin portion.
The strands of wire may be formed with a flat cross sectional shape.
The electrically-insulating resin portion may be formed on the apex portions of the coil ends by painting.
The electrically-insulating resin portion may be formed on the apex portions of the coil ends by spray painting.
The electrically-insulating resin portion may be formed on the apex portions of the coil ends by a fluid bed coating method.
The resin used in the electrically-insulating resin portion may have as its main component an epoxy resin having a predetermined viscosity such that the resin does not spread from the apex portions of the coil ends or adhere to portions of the strands of wire other than the apex portions while drying or setting.
A single-component resin setting at room temperature may be used for the electrically-insulating resin portion.
A two-component resin setting at room temperature may be used for the electrically-insulating resin portion.
A thermosetting epoxy resin powder paint may be used for the electrically-insulating resin portion.
The strands of wire may be composed of coil segments being electrically-insulated electrical conductors formed into a general U shape, and each of the winding sub-portions may be constructed by inserting the coil segments into slots a predetermined number of slots apart so as to form different layers relative to a slot depth direction and bending and joining free ends of the coil segments extending from the slots the predetermined number of slots apart requiring connection to each other.
The U-shaped coil segments may be inserted into the slots from one axial end of the stator core.
The strands of wire may be continuous wires composed of electrically-insulated electrical conductors.
The winding sub-portions may be constituted by at least one winding assembly composed of a pair of first and second winding groups, the first winding group including a number of first winding sub-portions each having one turn constructed by winding one of the electrically-insulated strands of wire so as to fold back outside the slots at axial end surfaces of the stator core and alternately occupy an inner layer and an outer layer in a slot depth direction within the slots at intervals of the predetermined number of slots, the first winding sub-portions being disposed at a pitch of one slot from each other and being equal in number to the predetermined number of slots, and the second winding group including a number of second sub-portions each having one turn constructed by winding one of the strands of wire so as to fold back outside the slots at axial end surfaces of the stator core and alternately occupy an inner layer and an outer layer in a slot depth direction within the slots at intervals of the predetermined number of slots and so as to be inversely wound and offset by an electrical angle of 180xc2x0 relative to the first sub-portions, the second sub-portions being disposed at a pitch of one slot from each other and being equal in number to the predetermined number of slots.